We are studying the organization of two families of genes in the budding yeast Saccharomyces cerevisiae: the histone genes and the ribosomal protein genes. Recombinant DNA molecules have been isolated which contain ribosomal protein genes; other recombinant DNA molecules contain histone genes. At the present time no recombinant DNA molecule has been identified which containes more than one ribosomal protein gene. Also, the genes for histones H3 and H4 are not present on the molecules which contain histones H2a and H2b. These coordinatley controlled genes demonstrate less linkage than one might expect and less linkage than is found in E. coli (for ribosomal protein genes) and less than is found in metazoans (for the histone genes). These plasmids are being further characterized.